Who in the civilized world could disagree with Trump’s expression of revulsion at the slaughter that killed dozens, included infants? And who could argue that action was warranted to deter a recurrence?

The message from the 59 Tomahawk missiles that inflicted significant damage on a Syrian air base was clear: This was a line that must never be crossed.

Obliteration of 20 Syrian warplanes is the simple part; to view it in isolation would be reckless in the extreme.

This is a conflict that could mutate in an instant.

The saying “the enemy of my enemy is my friend” does not even begin to capture the complexity of the civil war. Assad is merely one of the bad actors in Syria. His regime has been fighting the Islamic State, whose destruction is supposed to be Trump’s No. 1 global priority. One of Syria’s allies is Iran.

The other, of course, is Russia. Until Friday, the U.S. and Russia had agreed to exchange information about air operations in Syria to avoid accidental clashes. Russia has now halted such communication, leaving a perilous situation with forces of the two countries operating in proximity.

Assad’s regime has been aided immensely by the Russian military. The Russians failed, whether through incompetence or complicity, to fulfill their commitment to assure the elimination of Syria’s chemical weapons. Any credible U.S. policy to deter Assad would necessarily include pressure — such as heightened sanctions — on Russia to restrain its ally’s inhumanity.

Then there are the refugees. How can Trump reconcile his poignant words about the horror in Syria with his travel ban that blocks all refugees from that nation?

It’s hard to escape the impression that Trump is following his visceral instincts in the absence of a coherent vision for how to intervene without creating the next quagmire.

As a citizen, Trump cautioned President Barack Obama in 2013 against attacking Syria, after the last major poison gas attack on Assad’s own people. As a presidential candidate, Trump warned that opponent Hillary Clinton “wants to start a shooting war in Syria, in conflict with a nuclear-armed Russia, which could lead to World War III.”

Before the attack, Secretary of State Rex Tillerson had suggested shortly before Syrian forces unleashed the banned nerve agent on civilians that the future of Assad’s regime “will be decided by the Syrian people.” After the missile strikes, Tillerson said: “I would not in any way attempt to extrapolate that to a change in our policy.”

But is there a policy? Americans need to know, and Congress needs to be fully engaged, before the next moment of crisis prods Trump to act again in a civil war he had pledged to avoid.